1. Field
The invention relates to cladding composed of a multilayer composite for use in high temperature environments to serve as a barrier to protect the contents of the cladding, and methods of making the composites. More particularly, the invention relates to a multilayer composite fuel cladding for use in a reactor having water, liquid metal or liquid salt coolant.
2. Description of Related Art
A power reactor can include a reactor core having a large number of fuel assemblies, each of which is composed of a plurality of elongated fuel elements or fuel rods. Fuel assemblies vary in size and design depending on the desired size of the core and the size of the reactor. The fuel rods each contain fissile fuel material, such as, fuel pellets containing uranium with some amount of fissile U235 or U233 and/or plutonium. Fission of the fissile components causes heat generation. A coolant, such as water, liquid salt, gas or a liquid metal, e.g., lead, is pumped through the reactor core to extract the heat generated in the reactor core for the production of useful work such as electricity.
Each of the fuel rods has a cladding that acts as containment to hold the radioactive fuel material and to separate the fuel material from the coolant medium. Further, during operation, fission generates gaseous and volatile and non-volatile fission products that are highly radioactive, which are also restrained by the cladding. In conventional metallic cladding systems, irradiation over time causes damage to the metal in terms of hardening and embrittlement and material swelling.
FIG. 1 illustrates a prior art fuel cladding design which shows a stack of fuel pellets 10, a zirconium-based cladding 12, a spring hold down device 14, and end plugs 16.
Recent developments in the art have provided fuel rod cladding composed of a ceramic-containing material, such as silicon carbide (SiC). SiC has been shown to exhibit desirable properties in beyond design basis accidents, e.g., at temperatures greater than 1200° C. in light water reactors and, therefore, may be considered a suitable material of construction for nuclear fuel rod claddings. However, maintaining fission gas impermeability during flexing induced by handling or accidents or natural phenomena, such as earthquakes, is difficult due to the natural inelasticity of ceramic materials generally. Fastening end plugs on SiC tubes in a high throughput, economic manner yielding a hermetic seal at temperatures beyond 1200° C. is also difficult.
There is a desire in the art to provide a cladding material that provides high temperature mechanical strength and stability, swelling resistance and corrosion resistance, while providing protection and hermeticity to an external environment. There has not been found a single material that can provide all of the desirable properties for a cladding. Thus, an object of the invention is to provide a composite that includes more than one material, each exhibiting a different property that is advantageous for a cladding.